Background:

Full sized Dell Optiplex 745 tower.  Shipped with 1 HDD, and I installed another myself.  The drive I installed appears to be intermittently failing - doesn't appear in BIOS, and therefore disappears from Logical Disk Manager, My Computer, etc.  The HDD light stays on while the drive is not functional.

Cause and Resolution:

Since I didn't have a right-angled adapter on my SATA cable, I used a regular cable.  It didn't work so hot after about 8-12 mos of being crushed at a strange angle.

Can't say I'm surprised.

Bought a SATA cable with a right angled plug for $2.87 from DirectCanada via http://www.directcanada.com/products/?sku=1440142479C.  The cable is only 18" so it just reaches from the SATA plug.  I'd suggest something slightly longer if you're doing it, but this cable works fine.  Fits snugly, but not too much slack left in the cable.  Certainly not dangerous; you can easily swap some cables between devices around so that it works.